Skip lock file write when content unchanged to preserve timestamps

[Copilot]

Problem

Compiling workflows with only markdown changes (no frontmatter changes) rewrites lock files with identical content, updating timestamps and causing git to flag them as modified. This triggers false warnings about uncommitted files.

Changes

Compiler behavior (pkg/workflow/compiler.go)

• Compare generated lock file content with existing file before writing
• Skip write operation if content identical, preserving timestamp
• Only write when content differs

Test coverage (pkg/workflow/compiler_skip_write_test.go)

• Verify timestamp preservation when markdown-only changes
• Verify timestamp update when frontmatter changes
• Verify lock file creation when missing

Result

# Change only markdown content
$ vim workflow.md  # Edit description, no frontmatter change
$ gh aw compile workflow.md
✓ workflow.md (25.0 KB)

$ git status
Changes not staged for commit:
  modified: workflow.md
# Lock file not shown - content unchanged, timestamp preserved

# Change frontmatter
$ vim workflow.md  # Add permission
$ gh aw compile workflow.md
✓ workflow.md (25.1 KB)

$ git status
Changes not staged for commit:
  modified: workflow.md
  modified: workflow.lock.yml
# Both files shown - content changed, timestamp updated

Original prompt

Only changes to markdown were made so workflow did not produce a new yml on compile. But still we get a warning: https://docs.github.com/en/issues/planning-and-tracking-with-projects/learning-about-projects/about-projects If the frontmatter was not changed, not yml update should be required in the same commit/sha.

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